=begin pod

=TITLE class Proxy

=SUBTITLE Item container with custom storage and retrieval

    class Proxy {}

A Proxy is an object that allows you to execute whenever a value is retrieved
from a container (C<FETCH>) or when it is set (C<STORE>). Please note that
C<Proxy> can introduce mutability at places where it would break behaviour,
e.g. in C<Hash> keys.

To create a container that returns twice of what was stored in it, you do
something like this:

   sub double() is rw {
       my $storage = 0;
       Proxy.new(
           FETCH => method ()     { $storage * 2    },
           STORE => method ($new) { $storage = $new },
       )
    }
    my $doubled := double();
    $doubled = 4;
    say $doubled;       # OUTPUT: «8␤»

=head1 Methods

=head2 method new

    method new(:&FETCH!, :&STORE! --> Proxy:D)

Creates a new C<Proxy> object. C<&FETCH> is called with one argument (the
proxy object) when the value is accessed, and must return the value that the
fetch produces. C<&STORE> is called with two arguments (the proxy object, and
the new value) when a new value is stored in the container.

=end pod

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